The present invention relates to a paper separating unit to firmly prevent from more than one sheet of paper from being fed at a time, and an electronic printing apparatus which has the paper separating unit.
FIG. 1 is a perspective view of a paper feeding unit disposed in an electrophotographic device manufactured by FUMITSU LIMITED.
As shown in the perspective view of FIG. 1, this paper feeding unit is to prevent more than one sheet of paper P from being fed at a time (it is referred to as a multiple-feeding for later description in this specification), using a separate roller 3, as it picks up the paper P from a paper container where the paper is contained by a pick roller 1, then feeds the paper into a gap between a first feed roller 2 and the separate roller 3.
Therefore, the pick roller 1 and the first feed roller 2 are driven by a motor 4 in the same rotational direction in the present specification, rotational direction means the direction of angular displacement, not a tangential direction, (here the direction rotational such is that the lower perimeter of the pick roller 1 and the first feed roller 2 rotate from the pick roller 1 side to the first feed roller 2 side, i.e., clockwise on FIG. 1). On the other hand, while being pressed onto the first feed roller 2 with a predetermined magnitude of force, the separate roller 3 is driven by said motor 4, in the same direction as that of the first feed roller 2.
A torque limiter 5 is placed between this motor 4 and the separate roller 3, and when more than one sheet of the paper P attempt to pass through the gap between the first feed roller 2 and the separate roller 3, a rotational force generated by the separate roller 3 is applied on the second and lower sheets of paper P, and it generates a slip between the first paper P and the second paper P, then separates them apart, only the first sheet of paper P is pushed out from between the first feed roller 2 and the separate roller 3. However if only one sheet of paper P is fed into the gap between the first feed roller 2 and the separate roller 3, the separate roller 3 would be driven by the first feed roller 2 through this paper P without disturbing feeding of the paper P while it rotates in the opposite rotational direction as that of the first feed roller 2.
As the paper P which has passed through the gap between the first feed roller 2 and the separate roller 3 is fed to a second feed roller 6, the second feed roller 6 is driven to acceleratedly fed the paper P while rotation of said motor 4 in the first rotational direction is stopped.
Each of two one-way clutches 7, 8 is interposed between the first feed roller 2 and the motor 4 which drives the first feed roller 2, and between the pick roller 1 and the motor 4 respectively. After the motor 4 is stopped, the first feed roller 2 and the pick roller 1 are driven by the paper P which is acceleratedly fed by the second feed roller 6 in the paper feeding direction.
On the other hand, at the separate roller 3, friction is caused and it stops the separate roller 3 when the motor 4 is attempted to be rotated so that it gives a resisting force to the paper P, preventing the multiple-feeding.
However, it might happen that when the second feed roller 6 described above is driven, and, the paper P passing through the gap, the first feed roller 2 and the separate roller 3 is strongly pulled in its feeding direction, the motor 4 is driven via the separate roller 3 to rotate in the reverse rotational direction (the rotational direction opposite to the first rotational direction, i.e., counterclockwise on FIG. 1) by this paper P which is acceleratedly fed. In this case, since the first feed roller 2 and the pick roller 1 freely rotate in the paper feeding direction from the motor 4 due to the one-way clutches 7, 8, the multiple-feeding can occur as more than one sheet of paper P are fed into the gap between the first feed roller 2 and the separate roller 3.
Besides, to improve the capability of the paper separating, it is effective to increase a predetermined torque of the torque limiter 5; however, the higher the predetermined torque of the torque limiter 5 is set, the higher the probability of the reverse-rotation of the motor 4 becomes which moves along with the separate roller 3 when the second feed roller 6 accelerates feeding of the paper P.
As a method to prevent the reverse-rotation of the motor 4 as above, a method may be arise wherein the first feed roller 2 and the separate roller 3 are continuously driven without the accelerated feeding by the second feed roller 6 until the back end of the paper P passes through the gap between the first feed roller 2 and the separate roller 3.
However, in order to increase the operational speed of the apparatus, this method cannot be taken since it is advantageous to acceleratedly feed the paper P immediately after the front end of the paper P passes through the gap between the first feed roller 2 and the separate roller 3, when feeding the paper P out of the paper container which is located far from a printing portion, especially where the paper container is made multi-tiered.
As another method to prevent the multiple-feeding, a method may be arise wherein the rotational speed of the pick roller 1, the first feed roller 2, and the separate roller 3 is increased while accelerating the feeding of the paper P.
However this method cannot be taken either, since it inevitably causes enlargement of the drive system which drives those rollers and complication of their control devices, thus it cannot avoid a cost increase as a result.
Moreover, as a method other than described above to prevent the multiple-feeding, a method may be arise wherein i.e., fixing the separate roller 3 without driving it as disclosed in the Japanese Patent Application Laid-Open No. 6-171783 (1994). However, this method is not favorable since it causes a large friction on the paper P, and it has problems that it often allows several sheets of paper P to be completely overlapped when separating of the paper P has failed.